\end{cases}

(P^{'}, ℓ^{'}) = ⎩ ⎨ ⎧ (a P a, ℓ_{0}), (a D_{a} (P) a, ω_{a} (P) ℓ), (ϵ, a P ℓ), ℓ = a ℓ_{0}, ℓ \in / a Σ^{*}, D_{a} (P) defined, ℓ \in / a Σ^{*}, D_{a} (P) undefined .

Moreover,

S\in\mathsf{EPAL}_2\quad\Longleftrightarrow\quad \ell=\epsilon.

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